TECHNICAL FIELD
[0001] The present invention relates to a semiconductor device including a thin film diode
(Thin Film Diode: TFD), and a production method thereof.
BACKGROUND ART
[0002] In recent years, electronic equipment such as a display device or an image sensor
provided with an optical sensor portion utilizing a TFD has been developed.
[0003] Patent Document 1 discloses an image sensor in which an optical sensor portion utilizing
a TFD and a driving circuit utilizing a thin film transistor (Thin Film Transistor:
TFT) are provided on one and the same substrate. Patent Document 2 discloses a display
device provided with an optical touch panel. In this display device, an optical sensor
portion utilizing a TFD is provided in a display area of a liquid crystal display
device, so that an object such as a finger which touches the screen can be detected
by utilizing ambient light. In addition, Patent Document 3 discloses a display device
provided with an optical touch panel in which an object such as a finger which touches
the screen can be detected by utilizing not only ambient light incident on the display
panel but also reflected light of light from a backlight.
[0004] In the above-described display devices or in the image sensors, the TFD is formed
by utilizing a low-temperature poly-silicon film, for example. In this case, since
a semiconductor layer (the low-temperature poly-silicon layer) of the TFD is thin,
the semiconductor layer of the TFD cannot sufficiently absorb light having relatively
longer wavelength (e.g. red light) and there is some possibility that high sensitivity
cannot be attained. It is considered that the semiconductor layer of the TFD is made
thicker. However, if the semiconductor layer is made thicker, the process for crystallizing
an amorphous silicon film by laser crystallization or other means functions as the
rate-limiting factor. Accordingly, in view of the productivity, it is difficult to
greatly increase the thickness of the semiconductor layer of the TFD.
[0005] Therefore, conventionally, in order to improve effective sensitivity of an optical
sensor utilizing a TFD, it is necessary to increase the area of the light receiving
region by arranging a large number of diodes in parallel on a substrate. However,
if such a configuration is applied in a touch panel type display device, a large number
of diodes are arranged in the pixel area, thereby significantly deteriorating the
display characteristics.
[0006] On the contrary, Patent Document 4 suggests that a reflecting film is disposed via
an insulating film below the semiconductor layer of the TFD, and that the thickness
of the insulating film is optimized so as to increase the reflectance of light having
long wavelength (red light). Due to the suggestions, the document describes that it
is possible to increase the sensitivity of optical sensor to the red light.
CITATION LIST
PATENT LITERATURE
[0007]
Patent Document 1: Japanese Laid-Open Patent Publication No. 6-275807
Patent Document 2: International Publication WO 2008/132862
Patent Document 3: Japanese Laid-Open Patent Publication No. 2009-237286
Patent Document 4: Japanese Laid-Open Patent Publication No. 2004-71817
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0008] In a display device provided with an optical sensor portion, in addition to a TFD
used in the optical sensor portion, a TFT for pixel switching and a TFT for a driving
circuit are sometimes formed on one and the same substrate. Especially, in a display
device having a touch panel function or a scanner function, or in a display device
having both of the functions, two types of TFDs in which the detectable light wavelength
regions are different are sometimes formed on one and the same substrate. For example,
if a TFD for detecting visible light, a TFD for detecting infrared rays from a backlight,
and a TFT are formed on one and the same substrate, the sensing of an object or an
image which is in contact with the screen can be performed by utilizing not only the
ambient light (visible light) incident on the display panel, but also the infrared
rays emitted from the backlight. In such a display device, if a plurality of kinds
of TFDs and TFTs are to be simultaneously formed on the substrate, it is difficult
to individually optimize the device properties required for the TFDs and the TFTs.
[0009] The above-mentioned problem will be specifically described by way of an example of
a touch panel type display device provided with a visible light sensor for detecting
visible light, and an infrared-ray sensor for detecting infrared rays. In the display
device, a TFD used for the visible light sensor (a first TFD) and a TFD used for the
infrared-ray sensor (a second TFD) are formed on one and the same substrate. At this
time, if the structure suggested in Patent Document 4 is applied to the first TFD,
a reflecting structure including a reflecting film and an insulating film which are
the same as the first TFD is formed below the semiconductor layers of the second TFD
and the TFT. As a result, sufficient infrared rays are not incident on the second
TFD, thereby degrading the sensitivity of the infrared-ray sensor, or the visible
light is incident on the semiconductor layer of the TFT, so that there is some possibility
that an off-current of the TFT may be increased.
[0010] A conventional display device does not specifically take effective countermeasures
for increasing the sensitivity to infrared rays. Such countermeasures as that the
sensitivity of infrared-ray sensor is increased by increasing the intensity of illumination
of a backlight which emits light including infrared rays (referred to as an "IR backlight")
are carried out, but they may result in the increase in power consumption of backlight.
[0011] The present invention has been conducted in view of the above-described problems,
and the objective of the present invention is to provide a semiconductor device including
a first thin film diode for detecting light in a first wavelength region and a second
thin film diode for detecting light in a second wavelength region on one and the same
substrate in which the sensitivity of a sensor including the first thin film diode
with respect to the light in the first wavelength region and the sensitivity of a
sensor including the second thin film diode with respect to the light in the second
wavelength region are both obtained sufficiently.
SOLUTION TO PROBLEM
[0012] The semiconductor device of the present invention is a semiconductor device including:
a substrate; and a first thin film diode and a second thin film diode supported by
the substrate, wherein the first thin film diode includes a first semiconductor layer
and a first light blocking layer disposed on the substrate side of the first semiconductor
layer, the second thin film diode includes a second semiconductor layer and a second
light blocking layer disposed on the substrate side of the second semiconductor layer,
an insulating film is formed between the first semiconductor layer and the first light
blocking layer and between the second semiconductor layer and the second light blocking
layer, a thickness D1 of a portion of the insulating film positioned between the first
semiconductor layer and the first light blocking layer is different from a thickness
D2 of a portion of the insulating film positioned between the second semiconductor
layer and the second light blocking layer, light in a first wavelength region and
light in a second wavelength region including a wavelength longer than the maximum
wavelength of the first wavelength region are incident on the first and the second
semiconductor layers, the first and the second light blocking layers have surfaces
for reflecting the light in the first and the second wavelength regions, the intensity
of light in the first wavelength region incident on the first semiconductor layer
is higher than the intensity of light in the first wavelength region incident on the
second semiconductor layer, and the intensity of light in the second wavelength region
incident on the second semiconductor layer is higher than the intensity of light in
the second wavelength region incident on the first semiconductor layer.
[0013] In one preferred embodiment, the thickness D1 of the portion of the insulating film
positioned between the first semiconductor layer and the first light blocking layer
is smaller than the thickness D2 of the portion of the insulating film positioned
between the second semiconductor layer and the second light blocking layer.
[0014] In one preferred embodiment, the light in the first wavelength region includes visible
light, and the light in the second wavelength region includes infrared rays.
[0015] Preferably, the first semiconductor layer and the second semiconductor layer are
formed by using one and the same semiconductor film.
[0016] The insulating film may include: a lower film, made from a first insulating material,
which is formed to cover the first and the second semiconductor layers; and an upper
film, made from a second insulating material which is different from the first insulating
material, which is formed on the lower film to cover the second semiconductor layer
but not to cover the first semiconductor layer.
[0017] Alternatively, the insulating film may include: a lower film, made from a first insulating
material, which is formed to cover the second semiconductor layer but not to cover
the first semiconductor layer; and an upper film, made from a second insulating material
which is the same as or different from the first insulating material, which is formed
on the lower film to cover the first and the second semiconductor layers.
[0018] In one preferred embodiment, the thickness D1 and the thickness D2 are determined
respectively in such a manner that the ratio R
A(1) of the intensity of light in the first wavelength region incident on the first semiconductor
layer from the side of the insulating film to the intensity of light in the first
wavelength region incident on the insulating film after passing through the first
semiconductor layer from above the substrate is higher than the ratio R
B(1) of the intensity of light in the first wavelength region incident on the second semiconductor
layer from the side of the insulating film to the intensity of light in the first
wavelength region incident on the insulating film after passing through the second
semiconductor layer from above the substrate, and the ratio R
B(2) of the intensity of light in the second wavelength region incident on the second
semiconductor layer from the side of the insulating film to the intensity of light
in the second wavelength region incident on the insulating film after passing through
the second semiconductor layer from above the substrate is higher than the ratio R
A(2) of the intensity of light in the second wavelength region incident on the first semiconductor
layer from the side of the insulating film to the intensity of light in the second
wavelength region incident on the insulating film after passing through the first
semiconductor layer from above the substrate.
[0019] In one preferred embodiment, a thin film transistor supported by the substrate is
further provided, the thin film transistor includes a third semiconductor layer and
a third light blocking layer disposed on the substrate side of the third semiconductor
layer, the insulating film is formed between the third semiconductor layer and the
third light blocking layer, and a thickness D3 of a portion of the insulating film
positioned between the third semiconductor layer and the third light blocking layer
is substantially equal to the thickness D1.
[0020] In one preferred embodiment, a thin film transistor supported by the substrate is
further provided, the thin film transistor includes a third semiconductor layer and
a third light blocking layer disposed on the substrate side of the third semiconductor
layer, the insulating film is formed between the third semiconductor layer and the
third light blocking layer, and a thickness D3 of a portion of the insulating film
positioned between the third semiconductor layer and the third light blocking layer
is substantially equal to the thickness D2.
[0021] The production method of a semiconductor device of the present invention is a production
method of a semiconductor device including a substrate and a first and a second thin
film diodes supported by the substrate, including: (a) a step of forming a first and
a second light blocking layers on the substrate; (b) a step of forming an insulating
film to cover the first and the second light blocking layers, a portion of the insulating
film located on the second light blocking layer being thicker than a portion of the
insulating film located on the first light blocking layer; (c) a step of forming a
first island-like semiconductor layer as an active region of the first thin film diode
and a second island-like semiconductor layer as an active region of the second thin
film diode, the first island-like semiconductor layer being disposed in a region light-blocked
by the first light blocking layer and the second island-like semiconductor layer being
disposed in a region light-blocked by the second light blocking layer.
ADVANTAGEOUS EFFECTS OF INVENTION
[0022] According to the present invention, in a semiconductor device provided with a first
and a second thin film diodes in which wavelength regions of light to be detected
are mutually different on one and the same substrate, light in the wavelength region
to be detected by respective one of the thin film diodes can be efficiently incident
on the semiconductor layer of the corresponding thin film diode. As a result, both
of the effective sensitivities of a sensor utilizing the first thin film diode and
a sensor utilizing the second thin film diode can be obtained sufficiently.
[0023] Particularly, the present invention is preferably applied to a semiconductor device
provided with a diode for detecting visible light and a diode for detecting infrared
rays, thereby greatly increasing the sensing sensitivity to infrared rays as compared
with the prior art, while the sensing sensitivity to visible light is ensured.
[0024] According to the invention, the above-described semiconductor device can be easily
produced without increasing the number of production process steps and the production
cost, so that product downsizing, superior performance, and cost lowering can be realized.
[0025] The present invention is suitably applied to a display device having a touch panel
function, a display device having a scanner function, and a display device having
both of the functions.
BRIEF DESCRIPTION OF DRAWINGS
[0026]
[FIG. 1] FIG. 1 is a schematic sectional diagram showing the configuration of two thin film diodes
in a first embodiment of the present invention.
[FIG. 2] In FIG. 2, (a) is a schematic diagram exemplarily showing light in a first wavelength region (incident
light) L2 incident on an insulating film after passing through a semiconductor layer of a thin
film diode and light (reflected light) L3 of the light L2 incident on the semiconductor layer from the side of the insulating film, and (b) is a schematic diagram exemplarily showing light in a second wavelength region incident
on the insulating film after passing through the semiconductor layer of the thin film
diode and light L3 of the light L2 incident on the semiconductor layer from the side of the insulating film.
[FIG. 3] FIG. 3 is a graph showing the relationship between the thickness of an insulating film 14 and the sensitivity of a thin film diode.
[FIG. 4] In FIG. 4, (a) to (h) are schematic sectional process diagrams for illustrating the production method
of a first and a second thin film diodes in the semiconductor device in the first
embodiment of the present invention, respectively.
[FIG. 5] In FIG. 5, (a) to (d) are schematic sectional process diagrams for illustrating another production method
of the first and the second thin film diodes in the semiconductor device in the first
embodiment of the present invention, respectively.
[FIG. 6] FIG. 6 is a schematic sectional diagram showing two thin film diodes and a thin film transistor
in a semiconductor device in a second embodiment of the present invention.
[FIG. 7] FIG. 7 is a schematic sectional diagram showing two thin film diodes and a thin film transistor
in another semiconductor device in the second embodiment of the present invention.
[FIG. 8] FIG. 8 is a configuration diagram of an optical sensor type touch panel in a third embodiment
of the present invention.
[FIG. 9] FIG. 9 is a schematic plan diagram exemplarily showing a rear substrate in a touch panel
type liquid crystal display device in the third embodiment of the present invention.
[FIG. 10] In FIG. 10, (a) and (b) are a circuit diagram and a plan view, respectively, exemplarily showing the configuration
of an optical sensor portion in the third embodiment of the present invention.
[FIG. 11] FIG. 11 is a sectional diagram for illustrating the configuration of a thin film diode in
a reference example.
[FIG. 12] FIG. 12 is a schematic diagram for illustrating multiple reflection occurring between a semiconductor
layer and a light blocking layer in a thin film diode.
DESCRIPTION OF EMBODIMENTS
[0027] First, with reference to the accompanying drawings, the configuration of two thin
film diodes formed on one and the same substrate and the sensitivity of sensors utilizing
the respective thin film diodes will be described.
[0028] FIG.
11 is a sectional diagram showing a semiconductor device
1000 in a reference example. Herein, two thin film diodes
900A and
900B formed on a rear substrate of a liquid crystal display device are exemplarily described.
In this example, the diode
900A is used for a visible light sensor
1001 for detecting visible light, and the diode
900B is used for an infrared-ray sensor
1002 for detecting infrared rays.
[0029] The semiconductor device
1000 includes a substrate
1, diodes
900A and
900B formed on the substrate
1, a counter substrate
3, disposed opposite to the substrate
1, having color filters (not shown) and a CF light blocking portion
5, a liquid crystal layer
7 provided between the substrate
1 and the counter substrate
3, and a backlight
9 provided on the rear side of the substrate
1 (on the opposite side to the liquid crystal layer
7). The backlight
9 is an IR backlight for emitting light including infrared rays.
[0030] The diode
900A includes a light blocking layer
912A formed on the substrate
1, an insulating film
914 covering the light blocking layer
912A, and an island-like semiconductor layer
910A formed on the insulating film
914. The light blocking layer
912A is disposed so that the light from the backlight
9 will not be incident on the semiconductor layer
910A from the rear side of the semiconductor layer
910A. The semiconductor layer
910A includes a P-type region
910pA, an N-type region
910nA, and an intrinsic region
910iA, positioned between the P-type region
910pA and the N-type region
910nA, functioning as a light receiving region. Although not shown in the figure, the P-type
region
910pA is connected to an anode electrode, and the N-type region
910nA is connected to a cathode electrode. The diode
900B has the same configuration as that of the diode
900A.
[0031] The diodes
900A and
900B are fabricated on the substrate
1 by the common process. Therefore, the light blocking layers
912A and
912B are formed by patterning one and the same light blocking film. Similarly, the semiconductor
layers
910A and
910B are formed by patterning one and the same semiconductor film. In addition, the insulating
film
914 positioned between the semiconductor layer
910A and the light blocking layer
912A and between the semiconductor layer
910B and the light blocking layer
912B is common. Accordingly, the thickness of a portion of the insulating film positioned
between the semiconductor layer
910A and the light blocking layer
912A and the thickness of a portion of the insulating film positioned between the semiconductor
layer
910B and the light blocking layer
912B are usually equal (the thickness
D).
[0032] In the semiconductor device
1000, when the sensitivity of one of the sensors is high, the sensitivity of the other
sensor may disadvantageously be low. Thus, it is difficult to sufficiently obtain
both of the sensitivity of the visible light sensor
1001 and the sensitivity of the infrared-ray sensor
1002.
[0033] Hereinafter the reasons will be described.
[0034] The diodes
900A and
900B perform the sensing of light (incident light) incident on the intrinsic regions
910iA and
910iB of the semiconductor layers
910A and
910B after passing through the counter substrate
3. At this time, when the diode
900A is described exemplarily, part of the incident light is not absorbed by the intrinsic
region
910iA and is transmitted therethrough. The transmitted light is reflected from the surface
of the light blocking layer
912A disposed on the rear side of the intrinsic region
910iA. Part of the reflected light is incident on the intrinsic region
910iA again, and is absorbed therein. The remaining of the reflected light is further reflected
from an interface between the insulating film
914 and the semiconductor layer
910A, and then, reflected again from the light blocking layer
912A. As described above, part of light transmitted through the semiconductor layer
910A of the incident light is repetitively reflected between the semiconductor layer
910A and the light blocking layer
912A (multiple reflection). Similarly, in the diode
900B, multiple reflection of the incident light occurs between the semiconductor layer
910B and the light blocking layer
912B.
[0035] FIG.
12 is an enlarged sectional diagram schematically showing the multiple reflection of
light occurring between the semiconductor layers
910A and
910B and the light blocking layers
912A and
912B. The rays of light repetitively reflected between the semiconductor layers
910A and
910B and the light blocking layers
912A and
912B (light rays of multiple reflection) are mutually interfered. Accordingly, the reflectance
R with respect to the light of specific wavelength is increased, so that the amount
of light of the corresponding wavelength incident on the semiconductor layers
910A and
910B of the diodes is increased. For easy understanding, FIG.
12 shows the light
916A and
916B incident in the inclined direction with respect to the normal line of the surface
of the substrate
1. However, the multiple reflection also occurs for the light incident along the normal
line of the surface of the substrate
1.
[0036] Herein when the light of wavelength λ incident on the semiconductor layers
910A and
910B from the side of the counter substrate
3 is denoted by
L1, part of the incident light
L1 is absorbed by the semiconductor layers
910A and
910B. Light
L2 which is not absorbed of the incident light
L1 is transmitted through the semiconductor layers
910A and
910B and then incident on the insulating film
914. The light
L2 is multiple-reflected between the semiconductor layers
910A and
910B and the light blocking layers
912A and
912B. As a result, part of the light
L2 (reflected light
L3) is incident on the semiconductor layers
910A and
910B from the side of the insulating film
914. If the amplitudes of rays of wavelength λ are increased due to the interference of
the multiple-reflected rays, the ratio of the intensity
Ir of the reflected light
L3 incident on the semiconductor layers
910A and
910B from the side of the insulating film
914 to the intensity
Io of the light
L2 incident on the insulating film
914 of the incident light
L1 (hereinafter referred to as "reflectance
R") is increased. On the other hand, if the amplitudes of rays of wavelength λ are
reduced due to the interference of multiple-reflected rays, the reflectance
R is lowered.
[0037] The wavelength λ of rays for which the reflectance
R is increased is determined depending on the thickness
D and the refractive index
n of the insulating film
914, and represented by the following expression:
This expression
(1) represents the case where the light is incident from the normal direction of the
surface of the substrate
1. Accordingly, the thickness
D of the insulating film
914 is optimized based on the above expression
(1), so as to increase the reflectance
R with respect to the light of a specific wavelength λ. As a result, the amount of
light of the wavelength λ incident on the semiconductor layers
910A and
910B of the diodes can be increased.
[0038] In the diodes
900A and
900B shown in FIG.
11, the thicknesses D of the insulating film
914 are the same. For this reason, if the thickness
D of the insulating film
914 is selected so as to increase the reflectance
R of the light in a wavelength region to be detected by one of the diodes, the sensitivity
of the sensor including the diode can be improved. However, the reflectance
R of the light having the wavelength detected by the other diode is lowered, so that
the sensitivity of the sensor including the diode is degraded. As described above,
according to the configuration of the reference example, it is difficult to optimize
the respective characteristics of the diodes
900A and
900B in accordance with the application, and there is a problem that both of the sensitivity
of the visible light sensor
1001 and the sensitivity of the infrared-ray sensor
1002 cannot be sufficiently attained.
[0039] The inventors of the present invention found that in a semiconductor device provided
with two diodes in which wavelength regions of light to be detected are different
on one and the same substrate, the thicknesses
D of the insulating film positioned below the semiconductor layers of the diodes are
optimized respectively in accordance with the wavelength regions of light to be detected
by the respective diodes, thereby solving the above-mentioned problems. Accordingly,
by utilizing the multiple reflection of light as shown in FIG.
12, the light in the wavelength region to be detected by the diode can be efficiently
incident on the semiconductor layer of each diode. Therefore, both of the sensitivities
of the sensors of the respective diodes can be attained sufficiently.
[0040] In the conventional diodes
900A and
900B, the thickness
D of the insulating film cannot be optimized in one or both of the diodes. This may
cause a problem that the sensitivity is largely varied depending on the variation
of the thickness
D. On the other hand, according to the present invention, the thicknesses
D of the insulating film of both of the diodes are optimized, respectively, so that
it is possible to reduce the variation in sensitivity depending on the variation in
the thickness
D. For example, in the sensitivity curve shown in FIG.
3, in the vicinity of the maximum of the sensitivity, the variation in sensitivity depending
on the variation in the thickness of the insulating film is small. Therefore, a margin
for the thickness
D can be ensured.
(First Embodiment)
[0041] Hereinafter, a first embodiment of a semiconductor device of the present invention
will be described. The semiconductor device in the present embodiment is a liquid
crystal display device having an optical sensor portion utilizing a thin film diode,
for example.
[0042] FIG.
1 is a schematic sectional diagram showing two thin film diodes
100A and
100B in the semiconductor device in the present embodiment. For simplicity, the components
similar to those in FIG.
11 are designated by the same reference numerals, and the descriptions thereof are omitted.
[0043] A semiconductor device
200 in the present embodiment is provided with an optical sensor portion including a
first sensor
201 for detecting light in a first wavelength region and a second sensor
202 for detecting light in a second wavelength region. The first sensor
201 has a first thin film diode
100A, and the second sensor
202 has a second thin film diode
100B, respectively. The second wavelength region includes a wavelength longer than the
maximum wavelength of the first wavelength region. In other words, the maximum wavelength
of the second wavelength region is longer than the maximum wavelength of the first
wavelength region. The first wavelength region and the second wavelength region may
partially overlap.
[0044] The first thin film diode
100A includes a semiconductor layer
10A, and a light blocking layer
12A disposed on the side of the substrate
1 of the semiconductor layer
10A. Similarly, the second thin film diode
100B includes a semiconductor layer
10B, and a light blocking layer
12B disposed on the side of the substrate
1 of the semiconductor layer
10B. The semiconductor layers
10A and
10B are disposed in regions in which light from the side of the substrate
1 is blocked by the light blocking layers
12A and
12B, respectively. In this embodiment, the light blocking layers
12A and
12B not only block the light from the rear side of the substrate
1, but also function as reflecting layers for reflecting light incident from above the
substrate
1.
[0045] An insulating film
14 is formed between the semiconductor layer
10A and the light blocking layer
12A and between the semiconductor layer
10B and the light blocking layer
12B. A thickness
D1 of a portion of the insulating film
14 positioned between the semiconductor layer
10A and the light blocking layer
12A is different from a thickness
D2 of a portion of the insulating film
14 positioned between the semiconductor layer
10B and the light blocking layer
12B.
[0046] The thickness
D1 of the insulating film
14 is set in such a manner that the reflectance
R of light in the first wavelength region (the ratio of the intensity of light
L3 incident on the semiconductor layer
10A from the side of the insulating film
14 to the intensity of light
L2 incident on the insulating film
14 after being transmitted through the semiconductor layer
10A from above the substrate) is high. That is, the thickness
D1 of the portion of the insulating film
14 positioned between the semiconductor layer
10A and the light blocking layer
12A is determined so that the amplitudes of light rays in the first wavelength region
are mutually increased by multiple reflection and the intensity of light incident
again on the semiconductor layer
10A is increased. Specifically, the thickness
D1 can be obtained by the above expression
(1) in accordance with the refractive index
n of the insulating film
14 and the wavelength λ of the first wavelength region. Similarly, the thickness
D2 is set so that the reflectance
R of light in the second wavelength region is high. That is, the thickness
D2 is determined so that the amplitudes of light rays in the second wavelength region
are mutually increased by multiple reflection and the intensity of light incident
again on the semiconductor layer
10B is increased.
[0047] When the thicknesses
D1 and
D2 are obtained, if the same value is selected as the integer
k in the expression
(1), the thickness
D2 is larger than the thickness
D1. Since the integer
k can be arbitrarily selected, the thickness
D1 is sometimes larger than the thickness
D2. However, if the thickness of the insulating film
14 is increased, it takes a longer time to form the film, and it is sometimes difficult
for the multiple reflection to occur. For this reason, the integer
k is preferably equal to zero.
[0048] When the thicknesses
D1 and
D2 are optimized in the above-described way, as shown in FIG.
2(a), the ratio (reflectance)
RA(1) of the intensity of light (reflected light)
L3A(1) in the first wavelength region incident on the semiconductor layer
10A from the side of the insulating film
14 to the intensity of light (incident light)
L2A(1) in the first wavelength region incident on the insulating film
14 after passing through the semiconductor layer
10A from above the substrate
1 is higher than the ratio
RB(1) of the intensity of light
L3B(1) in the first wavelength region incident on the semiconductor layer
10B from the side of the insulating film
14 to the intensity of light
L2B(1) in the first wavelength region incident on the insulating film
14 after passing through the semiconductor layer
10B from above the substrate
1.
[0049] As shown in FIG.
2(b), the ratio
RB(2) of the intensity of light
L3B(2) in the second wavelength region incident on the semiconductor layer
10B from the side of the insulating film
14 to the intensity of light
L2B(2) in the second wavelength region incident on the insulating film
14 after passing through the semiconductor layer
10B from above the substrate
1 is higher than the ratio
RA(2) of the intensity of light
L3A(2) in the second wavelength region incident on the semiconductor layer
10A from the side of the insulating film
14 to the intensity of light
L2A(2) in the second wavelength region incident on the insulating film
14 after passing through the semiconductor layer
10A from above the substrate
1.
[0050] Accordingly, the intensity of light in the first wavelength region incident on the
semiconductor layer
10A in the first thin film diode
100A is higher than the intensity of light in the first wavelength region incident on
the semiconductor layer
10B in the second thin film diode
100B. In addition, the intensity of light in the second wavelength region incident on the
semiconductor layer
10B in the second thin film diode
100B is higher than the intensity of light in the second wavelength region incident on
the semiconductor layer
10A in the first thin film diode
100A. The "light incident on the semiconductor layers
10A and
10B" used herein includes, in addition to the light
L1 incident on the semiconductor layers
10A and
10B from above the semiconductor layers
10A and
10B (from the side of the counter substrate
3), the light
L3 incident on the semiconductor layers
10A and
10B from the side of the insulating film
14 by the multiple reflection shown in FIG.
12.
[0051] As described above, according to the present embodiment, by optimizing the thickness
of the insulating film
14, part of the light
L2 in a specific wavelength region emitted from above the substrate which is not absorbed
by but is transmitted through the semiconductor layers
10A and
10B in the thin film diodes
100A and
100B can be incident again on the semiconductor layers
10A and
10B by the multiple reflection. Accordingly, the amount of incident light in desired
wavelength regions can be respectively increased for the semiconductor layers
10A and
10B in the thin film diodes
100A and
100B. As a result, the output performances of sensors using the respective thin film diodes
100A and
100B can be improved.
[0052] According to the present embodiment, it is not necessary to increase the thicknesses
of the semiconductor layers
10A and
10B in order to improve the light sensitivities of the thin film diodes
100A and
100B, so that it is possible to easily form the semiconductor layers
10A and
10B by laser crystallization for the amorphous silicon film. In addition, the light sensitivities
can be improved without increasing the area of light receiving regions of the thin
film diodes
100A and
100B, so that it is possible to ensure high aperture ratio especially in the case where
the diodes
100A and
100B are formed in a display area.
[0053] The first wavelength region preferably includes visible light. The second wavelength
region preferably includes infrared rays. Accordingly, good sensing performance can
be exhibited over the wavelength region from infrared rays to visible light. In such
a case, as the backlight
9, an IR backlight which emits light including infrared rays is preferably used. Accordingly,
by utilizing the light from the backlight
9, the second sensor
202 utilizing the second thin film transistor
100B can perform the sensing of a finger, an image, or the like which comes into contact
with the panel surface.
[0054] Herein when the optimal value of the thickness
D1 is obtained from the above expression
(1), where the wavelength λ of visible light is 550 nm, the refractive index
n of the insulating film (for example, an SiO
2 film)
14 is 1.5, and the integer
k is 0, the thickness
D1 is about 92 nm. Alternatively, when the thickness
D2 is obtained where the wavelength λ of infrared rays is 780 nm, the refractive index
n of the insulating film
14 is 1.5, and the integer
k is 0, the optimal value of the thickness
D2 is about
130 nm.
[0055] FIG.
3 is a graph illustrating the relationship between the thicknesses
D1 and
D2 of the insulating film
14, and the sensitivity to the visible light and the infrared rays. Herein the reflectance
of a multi-layered thin film including a substrate, a light blocking layer, an insulating
film (two-layer structure of an SiN film and an SiO
2 film), and a semiconductor layer (a poly-silicon film) in this order is calculated
by utilizing Fresnel reflection coefficient, and the obtained reflectance of the multi-layered
thin film is regarded as the "sensitivity." As is seen from FIG. 3, the sensitivities
to visible light and infrared rays depend on the thicknesses
D1 and
D2 of the insulating film
14, respectively.
[0056] It is seen from FIG.
3 that the thickness
D1 for which the sensitivity to visible light is the highest is about 92 nm (k=0). It
is seen that the thickness
D2 for which the sensitivity to infrared rays is the highest is about 130 nm (k=0) and
about 390 nm (k=1). The relationship between the thickness of the insulating film
14 and the sensitivity in FIG.
3 is only exemplarily shown. The relationship can properly varied in accordance with
the materials (refractive indices) and the like of the insulating film
14, the light blocking layers
12A and
12B, and the semiconductor layers
10A and
10B.
[0057] From the result shown in FIG.
3, it is found that when the thicknesses
D1 and
D2 are optimized respectively, the sensitivity to infrared rays is about twice as high
as the sensitivity to visible light. It is considered that the reason why is that
the infrared rays are not absorbed by the semiconductor layer and easily transmitted
therethrough, and the amount of light rays which are incident again on the semiconductor
layer by multiple reflection and then absorbed is large, so that photo leakage current
generated in the semiconductor layer is greatly increased as compared with the case
where the light blocking layer is not provided.
[0058] In the present embodiment, the thin film diodes
100A and
100B are preferably formed on one and the same substrate by a common process. Accordingly,
the light blocking layers
12A and
12B are preferably formed by patterning one and the same light blocking film. In addition,
the semiconductor layers
10A and
10B are preferably formed by using one and the same semiconductor film, but alternatively
formed by using different semiconductor films. Although not shown in the figure, the
semiconductor device
200 in this embodiment may further include a thin film transistor.
[0059] In the display area of the semiconductor device (the display device)
200, the first sensor
201 including the first thin film diode
100A and the second sensor
202 including the second thin film diode
100B may be formed for each pixel, or for each pixel set having a plurality of pixels.
These sensors
201 and
202 may constitute separate sensors independently functioning, respectively. For example,
the first sensor
201 may function as a sensor for detecting visible light, and the second sensor
202 may function as a sensor for detecting infrared rays. At this time, the sensor for
detecting infrared rays may include a color filter for cutting out visible light.
[0060] Alternatively, the sensors
201 and
202 may be connected in parallel, thereby constituting one optical sensor portion. With
such a configuration, based on the output from one of the sensors
201 and
202 which detects light to be sensed, or which detects the light with higher sensitivity
(i.e. larger photo leakage current), the sensing can be performed. Accordingly, all
of light rays which can be detected by at least one of the sensors
201 and
202 can be detected, so that the detectable wavelength region can be significantly expanded.
The sensing is performed by using one of the sensors
201 and
202 with higher sensitivity to the light to be sensed, so that the sensitivity can be
enhanced as compared with the prior art.
[0061] It is preferred that the first wavelength region and the second wavelength region
may partially overlap. If there is no overlap portion, the range to be detected by
the optical sensor portion may disadvantageously be discontinuous. It is sufficient
that the second wavelength region may include a wavelength larger than the maximum
wavelength of the first wavelength region, and the shortest wavelength in the second
wavelength region may be shorter than the shortest wavelength in the first wavelength
region.
[0062] The thin film diodes
100A and
100B in this embodiment are produced in the following method, for example. In FIG.
4, (a) to
(h) are schematic sectional process diagrams for exemplarily illustrating the production
method of the thin film diodes
100A and
100B.
[0063] First, as shown in FIG.
4(a), on a substrate
1, light blocking layers
12A and
12B are formed. As the substrate
1, a low alkali glass substrate or a quartz substrate can be used. In this embodiment,
the low alkali glass substrate is employed. In this case, heat treatment at temperatures
lower than a glass strain point by about 10 to 20°C may be previously performed.
[0064] The light blocking layers
12A and
12B are located so as to block the light from the back side of the substrate
1 to the first and the second thin film diodes. The light blocking layers
12A and
12B can be formed by patterning a metal film or the like. In the case of the metal film,
in view of heat treatment in a succeeding production process, a film of a metal with
high melting point such as tantalum (Ta), tungsten (W), molybdenum (Mo), or the like
may preferably be used. In this embodiment, an Mo film is formed by sputtering, and
patterned, thereby forming the light blocking layers
12A and
12B. The thicknesses of the light blocking layers
12A and
12B are 100 to 200 nm, and preferably 150 to 200 nm. In this embodiment, the thicknesses
are 100 nm, for example.
[0065] Next, as shown in FIG.
4(b), a first insulating film
14L is formed so as to cover the substrate 1 and the light blocking layers
12A and
12B. Herein an SiO
2 film (the refractive index n: 1.46), an SiNO film (the refractive index n: 1.67),
or the like is formed as the first insulating film
14L by plasma CVD, for example.
[0066] Next, as shown in FIG.
4(c), on the first insulating film
14L, a photo mask
22 is formed so as to cover one of the light blocking layers (the light blocking layer
12B herein) and so as not to cover the other light blocking layer (the light blocking
layer
12A herein).
[0067] Next, as shown in FIG.
4(d), a portion of the first insulating film
14L which is not covered with the photo mask
22 is removed by etching. Thereafter, the photo mask
22 is removed.
[0068] Thereafter, as shown in FIG.
4(e), a second insulating film
14U is formed so as to cover both of the light blocking layers
12A and
12B. Herein an SiO
2 film (the refractive index n: 1.46), an SiNO film (the refractive index n: 1.67),
or the like is formed as the second insulating film
14U by plasma CVD, for example. The material of the second insulating film
14U may be the same as that of the first insulating film
14L, but alternatively be different. In this way, the insulating film
14 constituted by the first and second insulating films
14L and
14U is obtained.
[0069] In this embodiment, a portion of the insulating film
14 positioned on the light blocking layer
12A is constituted only by the second insulating film
14U. The thickness
D1 of the second insulating film
14U is 92 nm, for example. On the other hand, a portion of the insulating film
14 positioned on the light blocking layer
12B is constituted by the first and the second insulating films
14L and
14U. Herein the first insulating film
14L is formed by the same material as that of the second insulating film
14U. The total thickness
D2 of the first and the second insulating films
14L and
14U is 130 nm, for example. The thicknesses
D1 and
D2 are not limited to the above-described values, but may have values optimized based
on the expression
(1). In view of the parasitic capacitance and insulation properties of the semiconductor
layers
10A an
10B and the light blocking layers
12A and
12B, the thicknesses
D1 and
D2 are preferably 90 nm or more, for example, and more preferably 100 nm or more. If
the insulating film
14 is too thick, it takes a lot of time to form the insulating film
14, so that the thicknesses
D1 and
D2 are preferably 400 nm or less.
[0070] Next, as shown in FIG.
4(f), on the insulating film
14, a non-crystalline semiconductor film (herein an amorphous silicon film)
10a is formed. The a-Si film
10a is formed by a known method such as plasma CVD or sputtering. The thickness of the
non-crystalline semiconductor film
10a is not less than 20 nm and not greater than 70 nm, and preferably not less than 40
nm and not greater than 60 nm. In this embodiment, an a-Si film having the thickness
of 50 nm is formed by plasma CVD.
[0071] Thereafter, as shown in FIG.
4(g), a crystalline semiconductor film (herein a poly-silicon film) is formed by crystallizing
the non-crystalline semiconductor layer
10a, and then patterned, thereby obtaining semiconductor layers
10A and
10B. The crystallization of the non-crystalline semiconductor film
10a can be performed by laser crystallization. Alternatively, the crystallization may
be performed in such a way that after a catalyst element is added to the non-crystalline
semiconductor film
10a, annealing treatment is performed.
[0072] Next, as shown in FIG.
4(h), P-type regions
10pA and
10pB, and N-type regions
10nA and
10nB are formed in the semiconductor layers
10A and
10B. Specifically, a photo mask (not shown) is formed so as to expose only regions to
be P-type regions in the semiconductor layers
10A and
10B, in this condition, P-type impurity (e.g., boron) is injected. As a result, the P-type
regions
10pA and
10pB are obtained. Then a photo mask (not shown) is formed so as to expose only regions
to be N-type regions in the semiconductor layers
10A and
10B, and in this condition, N-type impurity (e.g., phosphorous) is injected. As a result,
the N-type regions
10nA and
10nB are obtained. The remaining regions of the semiconductor layers
10A and
10B in which the P-type regions and the N-type regions are not formed constitute intrinsic
regions
10iA and
10iB. In this specification, "the intrinsic region" indicates a region, sandwiched between
the P-type region and the N-type region, having lower impurity concentration (i.e.,
higher resistance) than the P-type and N-type regions. Accordingly, the intrinsic
region may be a region of intrinsic semiconductor or a region in which P-type or N-type
impurity is injected with lower concentration than in the P-type regions or the N-type
regions. Although not shown in the figure, after the above-described P-type and N-type
impurity injecting processes, heat treatment is performed under an inert atmosphere,
for example, under an atmosphere of nitrogen, so that the P-type regions
10pA and
10pB and the N-type regions
10nA and
10nB are activated.
[0073] Alternatively, before the P-type and N-type impurity injecting processes, an insulating
film for covering the semiconductor layers
10A and
10B may be formed. In such a case, the injection of impurity can be performed from above
the insulating film (through doping).
[0074] The production method of the thin film diode in this embodiment is not limited to
the method shown in FIG.
4. In FIG.
5, (a) to
(d) are schematic sectional process diagrams for illustrating another example of the
production method of the thin film diodes
100A and
100B.
[0075] First, as shown in FIG.
5(a), on a substrate
1, light blocking layers
12A and
12B are formed, and then, a first insulating film
14L is formed so as to cover the light blocking layers
12A and
12B. The light blocking layers
12A and
12B and the first insulating film
14L can be formed by the same methods as those described above with reference to FIG.
4(a) and FIG.
4(b). Herein as the first insulating film
14L, a silicon nitride film (an SIN film) is formed by plasma CVD. The refractive index
n of the SIN film is about 2.0.
[0076] Then, as shown in FIG.
5(b), on the first insulating film
14L, a first insulating film
14U is formed. Herein as the second insulating film
14U, a TEOS (Tetraethyl-Ortho-Silicate) film is formed by plasma CVD. The refractive index
n of the TEOS film is about 1.39.
[0077] The material of the second insulating film
14U may be the same as that of the first insulating film
14L, but may be preferably different from each other. It is preferred that the materials
of the respective insulating films
14L and
14U and an etchant may be selected so that only the second insulating film
14U is selectively etched in an etching process performed subsequently, i.e., so that
the etch selectivity to the etchant is high.
[0078] Next, as shown in FIG.
5(c), on the second insulating film
14U, a photo mask
24 is formed so as to cover one of the light blocking layers (the light blocking layer
12A herein) and so as not to cover the other light blocking layer (the light blocking
layer
12B herein).
[0079] Next, as shown in FIG.
5(d), a portion of the second insulating film
14U which is not covered with the photo mask
24 is selectively removed by etching. Herein buffered hydrogen fluoride (BHF) is used
as the etchant. After the etching, the photo mask
24 is removed. In this way, an insulating film
14 constituted by the first and the second insulating films
14L and
14U is obtained.
[0080] In this embodiment, a portion of the insulating film
14 positioned on the light blocking layer
12A is constituted only by the first insulating film (the SIN film)
14L. The thickness
D1 thereof is 92 nm, for example. On the other hand, a portion of the insulating film
14 positioned on the light blocking layer
12B is constituted by the first and the second insulating films
14L and
14U, and the total thickness
D2 is 130 nm, for example. Similarly to the method described above with reference to
FIG.
4, the thicknesses
D1 and
D2 are not limited to the above-mentioned thicknesses, but are optimized respectively
based on the expression
(1) in the range of not less than 90 nm and not greater than 400 nm.
[0081] Thereafter, although not shown in the figure, after semiconductor layers
10A and
10B are formed on the insulating film
14 by the same method as that described above with reference to
(f) to
(h) in FIG.
4, P-type regions
10pA and
10pB, N-type regions
10nA and
10nB, and intrinsic regions
10iA and
10iB are formed in the semiconductor layers
10A and
10B, respectively.
[0082] In the process described above with reference to FIG.
4 and FIG.
5, crystalline semiconductor layers are formed as the semiconductor layers
10A and
10B. Alternatively, the semiconductor layers
10A and
10B may be non-crystalline layers, or may be microcrystalline silicon layers.
[0083] In addition, in the above-described process, the insulating film
14 is formed from the two-layered insulating film. Alternatively, the insulating film
14 may be a single layer, or may have a layered structure including three or more layers.
In the case where the insulating film
14 having a multi-layered structure is to be formed, instead of the expression
(1), thicknesses of respective layers constituting the insulating film
14 can be optimized by using known conditions for interference by multi-layer films.
(Second Embodiment)
[0084] Hereinafter with reference to the drawings, a second embodiment of the semiconductor
device of the present invention will be described. The semiconductor device in the
second embodiment is different from the first embodiment in that in addition to the
two types of thin film diodes, a thin film transistor is formed on one and the same
substrate. The present embodiment can be applied to an active matrix display device
having an optical sensor portion such as a touch sensor, a scanner, or the like. The
two types of thin film diodes may be connected in parallel, so as to constitute an
optical sensor portion. The thin film transistor may be a pixel switching TFT disposed
for each pixel in a display area of a display device, or may be a TFT for a circuit
which constitutes a driving circuit in an area other than the display area (in a frame
area). Alternatively, the thin film transistor may be a signal taking-out TFT used
in the optical sensor portion.
[0085] FIG.
6 is a schematic sectional diagram showing thin film diodes
300A and
300B, and a thin film transistor
300C in a semiconductor device
400 in this embodiment.
[0086] The semiconductor device
400 includes a substrate
1, the thin film diodes
300A and
300B formed on the substrate
1, and the thin film transistor
300C formed on the substrate
1. In this embodiment, the thin film diode
300A is used for a visible light sensor
401 for detecting visible light, and the thin film diode
300B is used for an infrared-ray sensor
402 for detecting infrared rays. The thin film diodes
300A and
300B have the same structures as those of the thin film diodes
100A and
100B shown in FIG.
1, respectively. For the simplicity, the same components as those in FIG.
1 are designated by the same reference numerals, and the descriptions thereof are omitted.
[0087] The thin film transistor
300C has a light blocking layer
12C, a semiconductor layer
10C, and a gate electrode (not shown) disposed on the semiconductor layer
10C via a gate insulating film. Although not shown, the semiconductor layer
10C has a source region, a drain region, and a channel region located between these regions.
The gate electrode is disposed on the channel region. An insulating film
14 is formed between the light blocking layer
12C and the semiconductor layer
10C. A thickness
D3 of a portion of the insulating film
14 positioned between the light blocking layer
12C and the semiconductor layer
10C is equal to the thickness
D1 of a portion thereof positioned between the light locking layer
12A and the semiconductor layer
10A.
[0088] The reflectance of the thin film diode
300A and the reflectance of the thin film diode
300B in the semiconductor device
400 are similar to those of the thin film diodes
100A and
100B shown in FIG.
2(a) and FIG.
2(b), respectively. The reflectance of the thin film transistor
300C is similar to the reflectance of the thin film diode
300A.
[0089] If the "light in the first wavelength region" shown in FIG.
2(a) includes visible light, the reflectance of light in the first wavelength region of
the thin film diode
300A and the thin film transistor
300C is similar to the reflectance of light in the first wavelength region of the thin
film diode
100A. The reflectance of light in the first wavelength region of the thin film diode
300B is similar to the reflectance of light in the first wavelength region of the thin
film diode
100B. In other words, the ratio (reflectance)
RA(1) of the intensity of light (reflected light)
L3A(1) in the first wavelength region (herein visible light) incident on the semiconductor
layers
10A and
10C from the side of the insulating film
14 to the intensity of light (incident light)
L2A(1) in the first wavelength region incident on the insulating film
14 after passing through the semiconductor layers
10A and
10C from above the substrate
1 is higher than the ratio
RB(1) of the intensity of light
L3B(1) in the first wavelength region incident on the semiconductor layer
10B from the side of the insulating film
14 to the intensity of light
L2B(1) in the first wavelength region incident on the insulating film
14 after passing through the semiconductor layer
10B from above the substrate
1.
[0090] On the other hand, if "the light in the second wavelength region" shown in FIG.
2(b) includes infrared rays, the reflectance of light in the second wavelength region
of the thin film diode
300A and the thin film transistor
300C is similar to the reflectance of light in the second wavelength region of the thin
film diode
100A. The reflectance of light in the second wavelength region of the thin film diode
300B is similar to the reflectance of light in the second wavelength region of the thin
film diode
100B. In other words, the ratio
RB(2) of the intensity of light
L3B(2) in the second wavelength region incident on the semiconductor layer
10B from the side of the insulating film
14 to the intensity of light
L2B(2) in the second wavelength region incident on the insulating film
14 after passing through the semiconductor layer
10B from above the substrate
1 is higher than the ratio
RA(2) of the intensity of light
L3A(2) in the second wavelength region incident on the semiconductor layers
10A and
10C from the side of the insulating film
14 to the intensity of light
L2A(2) in the second wavelength region incident on the insulating film
14 after passing through the semiconductor layers
10A and
10C from above the substrate
1.
[0091] Accordingly, the intensity of visible light incident on the semiconductor layers
10A and
10C of the thin film diode
300A and the thin film transistor
300C is higher than the intensity of visible light incident on the semiconductor layer
10B of the thin film diode
300B, but the intensity of infrared rays incident on the semiconductor layers
10A and
10C is lower than the intensity of infrared rays incident on the semiconductor layer
10B.
[0092] According to the present embodiment, the following merits can be attained.
[0093] In order to reduce the off-current of the thin film transistor
300C, it is necessary to suppress the amount of light incident on the semiconductor layer
10C as small as possible. In the example shown in FIG.
6, the thickness
D3 of the insulating film
14 is equal to the thickness
D1. The thickness
D1 is set so that the reflectance
R with respect to the visible light is high and the reflectance
R with respect to the infrared rays is low, for example. Accordingly, the intensity
of the infrared rays incident on the semiconductor layer
10C from the side of the insulating film
14 due to the multiple reflection is low. Therefore, the off-current due to the light
incident on the semiconductor layer
10C can be reduce in the case where the off-current caused by the infrared rays incident
on the semiconductor layer 10C is more serious than the off-current caused by the
visible light.
[0094] FIG.
7 is a schematic sectional diagram showing another example of the semiconductor device
in this embodiment. In a semiconductor device
500 shown in FIG.
7, a thickness
D3 of an insulating film
14 between a semiconductor layer
10C and a light blocking layer
12C of a thin film transistor
300C' is equal to the thickness
D2 of the insulating film
14 between the semiconductor layer
10B and the light blocking layer
12B of the thin film diode
300B. The thickness
D2 is set so that the reflectance
R with respect to the infrared rays is high and the reflectance
R with respect to the visible light is low, for example.
[0095] The reflectance of the thin film diode
300A and the reflectance of the thin film diode
300B in the semiconductor device
300 are similar to the reflectance of the thin film diode
100A and the reflectance of the thin film diode 100B, respectively, shown in FIG.
2(a) and FIG.
2(b). Herein "the light in the first wavelength region" shown in FIG.
2(a) includes visible light, and "the light in the second wavelength region" shown in
FIG.
2(b) includes infrared rays. The reflectance of the thin film transistor
300C' is similar to the reflectance of the thin film diode
300B.
[0096] Accordingly, the intensity of infrared rays incident on the semiconductor layers
10B and
10C of the thin film diode
300B and the thin film transistor
300C' is higher than the intensity of infrared rays incident on the semiconductor layer
10A of the thin film diode
300A. However, the intensity of visible light incident on the semiconductor layers
10B and
10C is lower than the intensity of visible light incident on the semiconductor layer
10A.
[0097] As described above, in the thin film transistor
300C' shown in FIG.
7, the intensity of visible light incident on the semiconductor layer
10C from the side of the insulating film
14 is lowered due to multiple reflection. Accordingly, it is possible to reduce the
off-current due to the light incident on the semiconductor layer
10C in the case where the off-current caused by the visible light incident on the semiconductor
layer
10C is more serious than the off-current caused by the infrared rays.
[0098] It is sufficient that the thickness
D3 is set so as to suppress the sensitivity to light of a specific wavelength which
more greatly affects the off-current (photo leakage current) of the thin film diode
300C' and to effectively reduce the off-current. Accordingly, the thickness
D3 may be different from both of the thicknesses
D1 and
D2 of the insulating film
14 in the thin film diode. However, as shown in Fig.
6 and FIG.
7, the thickness
D3 is preferably equal to either one of the thicknesses
D1 and
D2. With such a configuration, the off-current can be reduced as compared with the prior
art without complicating the production process.
[0099] The thin film transistors
300C and
300C' in the present embodiment may have a single drain structure, or may alternatively
have an LDD (Lightly Doped Drain) structure or a GOLD (Gate-Overlapped LDD) structure.
The shape and the position of the light blocking layer
12C may be appropriately selected so that light is not incident on the semiconductor
layer
10C (at least the channel region of the semiconductor layer
10C) from the side of the substrate
1.
[0100] In the present embodiment, the light blocking layers
12A, 12B, and
12C are preferably formed by patterning one and the same light blocking film. In addition,
the semiconductor layers
10A, 10B, and
10C are preferably formed by patterning one and the same semiconductor film (e.g., a
poly-silicon film). Accordingly, the thin film diodes
300A and
300B and the thin film transistor
300C (or the thin film transistor
300C') can be fabricated on one and the same substrate without increasing the number of
production processes.
(Third Embodiment)
[0101] In the present embodiment, a display device provided with a sensor function. The
display device is configured by using a semiconductor device of any one of the above-described
embodiments.
[0102] The display device provided with the sensor function in the present embodiment is,
for example, a liquid crystal display device with a touch sensor which includes a
display area and a frame area located around the display area. The display area has
a plurality of display portions (pixels) and a plurality of optical sensor portions.
Each display portion includes a pixel electrode and a pixel switching TFT, and each
optical sensor portion includes two types of optical sensors for mutually different
wavelength regions to be detected. Each optical sensor includes a TFD. In the frame
area, a driving circuit for display is provided so as to drive each display portion,
and a TFT for a driving circuit is utilized for the driving circuit. The pixel switching
TFT and the TFT for a driving circuit, and the TFD of the optical sensor portion are
formed on one and the same substrate. In the display device of the present invention,
it is sufficient that at least the pixel switching TFT among the TFTs used in the
display device may be formed on one and the same substrate on which the TFD of the
optical sensor portion is formed by the above-described method. For example, the driving
circuit may be separately provided on another substrate.
[0103] In the present embodiment, the optical sensor portion is disposed adjacent to a corresponding
display portion (e.g., a pixel of primary color). For one display portion, one optical
sensor portion may be disposed, or a plurality of optical sensor portions may be disposed.
Alternatively, for each set of a plurality of display portions, one optical sensor
portion may be disposed. For example, for a color display pixel constituted by pixels
of three primary colors (RGB), one optical sensor portion can be provided. As described
above, the number (the density) of optical sensor portions for the number of display
portions can be appropriately selected in accordance with the resolution.
[0104] If the color filters are provided on the side of an observer of the optical sensor
portion, the sensitivity of the TFD which constitutes the optical sensor portion may
disadvantageously be degraded, so that it is preferred that the color filters may
not be provided on the side of the observer of the optical sensor portion.
[0105] In the case where the intensity of illumination of ambient light is high, the optical
sensor portion of this embodiment detects the shadow of an object which is in contact
with or comes closer to the screen (a finger pulp or the like) by utilizing the ambient
light. In the case where the intensity of illumination of ambient light is low, the
optical sensor portion detects infrared rays which are emitted from the backlight
and then reflected from the object.
[0106] Hereinafter with reference to the drawings, the configuration of the display device
in this embodiment will be described by way of an example of a touch panel liquid
crystal display device provided with a touch panel sensor.
[0107] FIG.
8 is a schematic sectional diagram showing an example of an active matrix type touch
panel liquid crystal display device.
[0108] A liquid crystal display device
600 includes a liquid crystal module
802, a backlight
801 disposed on the rear side of the liquid crystal module
802. The liquid crystal module
802 is constituted by a rear substrate
814 with translucency, a front substrate
812 disposed opposite to the rear substrate
814, and a liquid crystal layer
810 provided between the substrates
814 and
812. The liquid crystal module
802 has a plurality of display portions (pixels of primary colors). Each of the display
portions has a pixel electrode (not shown) and a pixel switching thin film transistor
805 connected to the pixel electrode. An optical sensor portion including a thin film
diode
806 is disposed adjacent to the respective color display pixel constituted by the display
portions of three primary colors (RGB). Alternatively, one optical sensor portion
may be disposed for two adjacent color display pixels (six display portions). Although
being omitted in this figure, the optical sensor portion includes at least one first
sensor which includes the thin film diode
806 and detects visible light with high sensitivity and at least one second sensor which
includes another thin film diode (not shown) and detects visible light with high sensitivity.
[0109] Color filters (not shown) are disposed on the side of the observer of each display
portion, but color filters are not disposed on the side of the observer of the optical
sensor portion. A light blocking layer
807 is disposed between the thin film diode
806 and the backlight
801. Accordingly, light
808 from the backlight
801 is blocked by the light blocking layer
807, so that it is not incident on the thin film diode
806 from the back side (i.e., from the side of the rear substrate
814). It is sufficient that the light blocking layer
807 may be disposed in such a manner that the light from the backlight
801 is not incident on an intrinsic region of the thin film diode
806.
[0110] In the optical sensor portion, the first sensor including the thin film diode
806 and the second sensor including another thin film diode are connected in parallel.
The first sensor performs the sensing of ambient light (visible light)
804. On the other hand, the second sensor performs the sensing of light of the light (infrared
rays)
808 from the backlight
801 which is reflected from a finger pulp or the like after passing through the liquid
crystal module
802.
[0111] FIG.
9 is a schematic plan view showing the rear substrate
814 of the display device in this embodiment. In the example shown in the figure, one
optical sensor portion is provided for two color display pixels of R, G, and B pixels.
[0112] The rear substrate
814 in this embodiment is provided with a plurality of R, G, and B pixels arranged in
a matrix and a plurality of optical sensor portions
700. Each pixel has a pixel switching thin film transistor
905 and a pixel electrode (not shown). Herein sets of pixels
909a and
909b constituted by adjacent R, G, and B pixels are referred to as "color display pixels."
In this embodiment, one optical sensor
700 is disposed for adjacent two color display pixels
909a and
909b.
[0113] The thin film transistor
905 has a dual gate LDD structure including, for example, two gate electrodes and an
LDD region. A source region of the thin film transistor
905 is connected to a source bus line
908 for pixel, and a drain region thereof is connected to a pixel electrode. The thin
film transistor
905 is turned on and off in accordance with a signal from a gate bus line
906 for pixel. Accordingly, a voltage is applied across a liquid crystal layer by the
pixel electrode and a counter electrode formed on a front substrate disposed opposite
to the rear substrate, and the alignment condition of the liquid crystal layer is
changed, thereby performing the display.
[0114] In this embodiment, an RST signal line
902 and an RWS signal line
904 are provided between adjacent two gate wirings
906. These lines
902 and
904 are formed by one and the same layer as the gate wiring
906. The optical sensor portion
700 is disposed between these lines
902 and
904.
[0115] In FIG.
10(a) and FIG.
10(b) are a circuit diagram and a plan view for illustrating the configuration of the optical
sensor portion
700 in this embodiment, respectively.
[0116] As shown in FIG.
10(a), the optical sensor portion
700 includes thin film diodes
701A and
701B, signal holding capacitors
702A and
702B, and a signal taking-out thin film transistor
703. The thin film diodes
701A and
701B and the thin film transistor
703 are disposed in regions defined by the source bus lines
908, and the RWS signal line
904 and the RST signal line
902, respectively.
[0117] As is seen from FIG.
10(b), the thin film diode
701A is provided with a semiconductor layer including a p-type region
710p, an n-type region
710n, and an intrinsic region
710i positioned between these regions
710p and
710n. The thin film diode
701B is provided with a semiconductor layer including a p-type region
711p, an n-type region
711n, and an intrinsic region
711i positioned between these regions
711p and
711n. Below the thin film diode
701A and the thin film diode
701B, light blocking layers are disposed, respectively, via an insulating film. The diodes
701A and
702B have the same configurations as those of the thin film diodes
100A and
100B shown in FIG.
1, respectively.
[0118] The signal holding capacitors
702A and
702B are configured by using the gate electrode layer and the semiconductor layer as their
electrodes, and the capacitance is formed by a gate insulating film.
[0119] The p-type region
710p in the thin film diode
701A is connected to the RST signal line
902, and n-type region
710n is connected to a lower electrode (an Si layer) in the signal holding capacitor
702A through which the n-type region
710n is connected to the RWS signal line
904. Similarly, the p-type region
711p in the thin film diode
701B is connected to the RST signal line
902, and the n-type region
711n is connected to a lower electrode (an Si layer) in the signal holding capacitor
702B through which the n-type region
711n is connected to the RWS signal line
904. Moreover, the n-type regions
710n and
711n are connected to a gate electrode layer in the signal taking-out thin film transistor
703. A source region of the signal taking-out thin film transistor
703 is connected to a VDD signal line
908VDD, and a drain region thereof is connected to an output signal line
908COL. The signal lines
908VDD and
908COL also function as source bus lines.
[0120] Next, the operation in optical sensing by the optical sensor portion
700 will be described.
[0121] (1) First, by the RWS signal line
904, an RWS signal is written into the signal holding capacitors
702A and
702B. Thus, plus electric fields are generated on the side of the n-type regions
710n and
711n in the optical sensor thin film diodes
701A and
701B, respectively, so as to be reverse bias condition with respect to the thin film diodes
701A and
701B.
[0122] (2) If photo leakage occurs in at least one of the thin film diodes
701A and
701B, charges are released to the side of the RST signal line
902 via the thin film diode. At this time, if photo leakage occurs in only one of the
thin film diodes, the current flows via the thin film diode only. If photo leakage
occurs in both of the thin film diodes, the current flows mainly via one of the thin
film diodes with larger photo leakage.
[0123] (3) Accordingly, the potential on the side of the n-type regions
710n and
711n lowers, and the gate voltage applied across the signal taking-out thin film transistor
703 is varied in accordance with the potential change.
[0124] (4) A VDD signal is applied from the VDD signal line
908VDD on the source side of the signal taking-out thin film transistor
703. When the gate voltage is varied as described above, the current value flowing to
the output signal line
908COL connected to the drain side is varied, so that the electrical signal can be taken
out from the output signal line
908COL.
[0125] (5) Thereafter, a current is caused to flow in the forward direction from the output
signal line
908COL to the thin film diodes
701A and
701B, and the RST signal is written into the signal holding capacitors
702A and
702B, so as to reset the potential of the signal holding capacitors
702A and
702B. At this time, the reset can be performed via one of the thin film diodes
701A and
701B with higher current driving force.
[0126] The operations of (1) through (5) are repeated while performing the scanning, so
that optical sensing by utilizing the ambient light and the light from the backlight
can be performed.
[0127] The configuration of the rear substrate in the touch panel liquid crystal display
device in this embodiment is not limited to that shown in FIG.
9. For example, a storage capacitor (Cs) may be disposed in each pixel switching TFT.
In the example shown in FIG.
9, one optical sensor portion is provided for two color display pixels (two pixel sets
of RGB pixels). Alternatively, one optical sensor portion may be disposed for one
color display pixel. Alternatively, in order to further increase the resolution, one
optical sensor portion may be provided for each RGB pixels. However, in such a case,
the aperture ratio is significantly reduced, so that there is a possibility that the
brightness of display may be reduced.
[0128] The semiconductor device in this embodiment is not limited to the touch panel liquid
crystal display device, but may be a display device with an image sensor function
or a fingerprint sensor function. The above-described optical sensor portion
700 can be used as an image sensor or a fingerprint sensor. In the case where the optical
sensor portion
700 is used as the image sensor or the fingerprint sensor, in order to detect an image
or fingerprints which are pressed against the screen, higher resolution is generally
required than the touch sensor. The resolution is increased in accordance with the
increase in number of optical sensor portions for the pixels. For this reason, the
number of optical sensor portions can be appropriately adjusted in accordance with
the application. As is shown in FIG.
9, if one optical sensor portion is disposed for two color display pixels, it is possible
to ensure sufficient resolution with which an image such as a name card can be read.
In addition, if a color filter is disposed on the side of an observer of the optical
sensor portion and light passing through the color filter is received by the optical
sensor portion, the optical sensor portion can function as a color image sensor.
[0129] In this embodiment, one optical sensor portion is constituted by connecting two thin
film diodes with different wavelength regions of light to be detected in parallel.
Alternatively, the two thin film diodes are not connected in parallel, but they may
be used as two optical sensors functioning independently.
[0130] As described above, the specific embodiments of the present invention have been described,
but the present invention is not limited to the above-described embodiments. Various
modifications based on the technical idea of the present invention can be realized.
For example, the semiconductor device of the present invention is not limited to a
display device provided with an optical sensor portion, but may be an image sensor.
Hereinafter the configuration of an image sensor to which the present invention is
applied will be briefly described.
[0131] The image sensor is provided with a plurality of light receiving portions arranged
in two dimensions, and an image information generating portion for generating image
information. Each of the light receiving portions may have the same configuration
as that of the display portion (the pixel) shown in FIG.
9 and FIG.
10. Each of the light receiving portions may be constituted by three pixels (RGB pixels).
Each of the light receiving portions includes the above-described optical sensor portion
700. The image information generating portion generates image information related to a
sensing signal generated in the optical sensor portion
700 in each light receiving portion and the position of the corresponding light receiving
portion. Accordingly, the image read by the image sensor can be formed or certificated.
INDUSTRIAL APPLICABILITY
[0132] The present invention can be widely applied to a semiconductor device provided with
an optical sensor portion utilizing a TFD, or electronic equipment in various fields
including such a semiconductor device. For example, the present invention may be applied
to a CMOS circuit or a pixel portion in an active matrix liquid crystal display device
or an organic EL display device. Such a display device can be utilized as, for example,
a display screen of a portable phone or a portable video game, a monitor of a digital
camera, or the like. Accordingly, the present invention can be applied to any electronic
equipment in which a liquid crystal display device or an organic EL display device
is incorporated.
[0133] The present invention can be particularly applied suitably to a display device such
as an active matrix liquid crystal display device and an organic EL display device,
an image sensor, an optical sensor, or electronic equipment in which they are combined.
Especially, it is advantageous that the present invention may be applied to a display
device provided with an optical sensor function utilizing a TFD, for example, a display
device provided with both of a touch panel function and a scanner function.
REFERENCE SIGNS LIST
[0134]
- 1
- substrate
- 3
- counter substrate
- 5
- CF light blocking portion
- 7
- liquid crystal layer
- 9
- backlight
- 10A, 10B
- semiconductor layer of thin film diode
- 10C
- semiconductor layer of thin film diode
- 10pA, 10pB
- P-type region
- 10nA, 10nB
- N-type region
- 10iA, 10iB
- intrinsic region
- 12A, 12B, 12C
- light blocking layer
- 14
- insulating film
- 100A, 100B, 300A, 300B
- thin film diode
- 300C, 300C'
- thin film transistor
- 200, 400, 500
- semiconductor device
- 201, 202
- sensor
- 401
- visible light sensor
- 402
- infrared-ray sensor